Most automobile engines include a chain transmission which transmits power through an endless chain engaged with a driving sprocket and a driven sprocket. In a typical transmission chain, as exemplified by chain 500 in FIG. 10, concave chain surfaces 511 and 551, that come into facing relationship with a chain guide, are formed respectively on the guide facing sides of inner link plates 510 and outer link plate 550. Lubricating oil is retained by these guide-facing concave surfaces 511 and 551 to reduce friction between the chain and the chain guides, which can include both an arc-shaped chain guide G1 and a straight chain guide G2. An example of such a chain transmission, including an arc-shaped chain guide and a straight chain guide, is described in United States Patent Publication 2006/0079363, published Apr. 16, 2006.
As seen in FIG. 10, the length of each such concave guide-facing surface 511 and 551, in the direction of the length of the chain, is at least as great as the chain pitch P, i.e., the distance between the centers of the pin holes 512 formed in the inner link plates 510, and between the centers of the pin holes 552 formed in the outer link plate 550.
As shown in FIG. 10, in the conventional transmission chain 500, because the lengths of the guide-facing concave surfaces 511 and 551 are respectively equal to or greater than the chain pitch P, tensile stress is concentrated at parts F of plate portions E, which are aligned with the centers of holes 512 of the inner link plates, in which bushings are press-fit, and with the centers of holes 552 of the outer link plates, in which connecting pins are press-fit. The plate portions E have a cutout shape, and stress, due to sliding contact between the chain and an arc-shaped chain guide G1 or a straight chain guide G2, acts on these plate portions E, causing fatigue fracture and chain breakage.
There has been a need for improvements in the strength of the plate portions E.
As shown in FIG. 10, since an inner link plate 510, or the outer link plate 550, comes into contact with a linear chain guide G2 at small contact regions Z, it is not possible to retain sufficient lubricating oil, and sliding resistance is generated in both regions Z, so that there is a possibility of failure of the link plates.
Since the guide-facing surfaces 511 and 551, formed on peripheral portions of the link plates are concave, an arc-shaped chain guide G1 can enter the concave guide-facing surfaces 511 and 551. The result is that the chain sinks toward the arc-shaped guide G1, causing slack to be generated in the chain and a possibility for the chain path to become unstable.
Accordingly, an object of the invention is to solve the above-described problems, and to provide a transmission chain in which sinking of a chain with respect to a convex surface of a chain guide is reduced so that the chain path is stabilized, in which the link plates have improved strength in the regains where tensile force is concentrated, and fatigue failure is liable to generate is improved, and lubricating oil is reliably retained between the chain guide and the plate so that improved endurance is achieved.